Featured Soil of the month - February Calcareous Loamy Earth
During the year of soils, each month we ask a soil researcher to select his or her favourite soil. Tim Overheu is the current Federal President of Soil Science Australia and Past President of the Western Australian Branch. Tim is a long serving soil surveyor in Western Australia and is passionate about all soils, so finding just one soil to call his favourite might have been a bit of challenge.
If you had to choose a special Australian soil type what would it be?
I started my career as a soil surveyor, initially working on a soil-landscape mapping project based in the regional community of Esperance, Western Australia. The work involved a ‘paddock by paddock’ grid style soil mapping exercise across the coastal sandplain and the southern mallee area -using poor quality black and white orthophotos as the reference base and a shovel, crowbar and auger; no enhanced colour imagery, digital ‘on the fly’ mapping tools or air conditioning back in those days.
I recall in my first year of this routine style of mapping, being fascinated by sodic texture contrast soils with massive columnar or prismatic subsoil structure, deep sands with humic-sesquioxide pans and the wonderful variety of mallee soils ranging from acid deep red sands through to gravelly calcareous loams. So, it probably comes as no surprise that I don’t actually have one favourite soil, but rather an interest in a range of soils that exhibit unusual characteristics.
While I’d love to ramble on about deep sand, for the purpose of highlighting just one soil of interest, I’ve chosen to write about a Calcareous Loam that features in the Salmon Gums area of Western Australia. While the Australian Soil Classification (ASC) classifies it as an Epihypersodic Regolithic Supracalcic Calcarosol, to the mallee locals it’s simply called Kopi or Fluff or a calcareous loam.
What are the main properties of this soil type?
This soil has a loose and powdery (fluffy) surface over a highly calcareous loam subsoil. The profile is strongly alkaline throughout and the subsoil is often high in salt. It usually occurs on level to gently undulating landscapes of the southern mallee country around communities of Mount Beaumont, Salmon Gums and Cascades.
Characteristic soil properties include:
- Alkaline and calcareous throughout (soft carbonate and calcareous nodules)
- Highly saline below 20 cm (EC often more than 200 mS/m)
- Sodic below 20 cm
- Fluffy, puffy soil material throughout
- Water repellent topsoil
Image 2. Typical native vegetation on a Calcareous Loamy Earth, Salmon Gums Western Australia
| Image 1. Calcareous Loamy Earth
(Beete soil series) Salmon Gums, Western Australia
|Image 3. Typical Salmon Gums landscape, illustrating the salt lake chains, where the Calcareous Loamy Earth (Beete soil series) is most common.|
Why do you find this soil type particularly interesting?
I find this soil fascinating because of its inherent unusual soil properties – including its high alkalinity and high salinity, together with its position in the landscape.
The soil and associated landscape is probably more related to the Nullarbor than it is to the South Coast mallee plain. The soil is commonly found in small patches mixed with other ‘mallee-type’ soils; often found near salt lakes, where it is highly saline; and often on the mounds adjacent the depressions of crabhole landscapes.
Another interesting feature I’ve observed is where the soil is located under native bush, the subsurface layers have fungal hyphae (not visible to the eye) or a very fine root mass that seems to hold the fluffy soft carbonate content together, sometimes making the soil feel like a very soft dough in your hands – where this feature occurs the subsurface layers are also often hydrophobic.
Do the properties of this soil type have consequences for its management, e.g. in terms of land use, soil quality, conservation
Where the native vegetation covering this soil has been cleared, and the land developed for agriculture, generally the soil yields poorly because of its highly alkalinity (pH 9.5+), inhibiting nutrient availability. Pasture cover is also often poor. The soil is marginal at best (sometimes unsuitable) for cereals – the limiting factors being boron toxicity, subsoil salinity and high alkalinity. It is unsuitable for grain legumes because of the alkalinity and risk of wind erosion. Salt tolerant shrubs grow well on this soil and may provide some (but limited) grazing for sheep. The soil is unsuitable for roaded catchments and conservation earthworks, and it is highly susceptible to wind erosion, as bare or exposed areas erode easily (depositing the fluffy, saline, and alkaline topsoil on surrounding soils). On the good side though, it is well drained, has good soil workability, and there is no risk of soil acidification.
Can you tell us your most memorable story concerning this soil type?
I am not sure about the etiquette, but I’m sure people have probably heard worse. I was once interviewed by a local journalist about the range of soils over the Esperance-Salmon Gums area. I was discussing the fascinating soils in the mallee area, in particular the ‘fluffy’ white loamy soils. I specifically asked the journalist to use local terms where possible for the soils. I also added some comment about the native vegetation in the area and the indicator species linked to the various soil associations. I recall I used the term Virgin bush for the terrific uncleared vegetation corridors. Anyway, to cut a long but not so funny story short, the Journalist did abide by my request to use the local soil terminology and the article was published in the West Australian and some regional newspapers with me referring to ‘Virgin Fluff’ multiple times through the article. Embarrassing, but I survived (learning a good lesson about what not to say to journalists). Meanwhile, I’m sure that journalist was probably having a good belly laugh somewhere.